Modern large-venue speaker systems used, for example, in theaters and concert halls, often require three or more kilowatts of audio power. The amplifiers available which meet such high power requirements are not only very large and heavy, but generally have limited capability of producing high frequency signals and higher harmonic distortion than low power amplifiers. In addition, the prior art high power amplifiers have shortcomings with respect to circuitry for (a) generating drive control and monitoring signals; (b) handling abnormal operating condition such as overload leading to system failure; and (c) handling reactive loads with minimum power dissipation.
The generation of monitoring signals is essential for remote system monitoring which is a new, but a growing requirement in modern multiple amplifier sound reinforcement systems. To achieve this, signals conveying information about the internal state of the amplifier must be developed within the amplifier and presented to an external interface. The creation of a monitor signal that represents the current delivered by the amplifier to its load has necessitated the use of shunts or current transformers and measurement circuitry dedicated to that purpose. Such shunts or transformers add to the cost.
Conventional power amplifiers do not use explicit drive control signals for controlling the separate bridge elements in a class B mode, for example. As a result, circuitry to protect the amplifier becomes more complex.
Prior art bridge audio amplifiers are disclosed in U.S. Pat. No. 3,808,545 which issued to G. Stanley in 1986, U.S. Pat. No. 3,383,613 which issued to J. F. Novak in 1968, and U.S. Pat. No. 2,821,639 which issued to R. L. Bright et al in 1958. Such amplifiers have one or more of the above shortcomings.
There is a need for a high power amplifier capable of reproducing signals over an extended bandwidth with low harmonic distortion which overcomes the shortcomings of the prior art amplifiers.